274 Proceedings of the Royal Society of Edinburgh. [Sess. 
and so on) for us to hail any newly discovered calcification as prima facie 
evidence of a primitive appendicular segment.* 
The first indubitable segment of the sympodite is very short, yet it 
forms a complete ring. Posteriorly and proximally it bears a groove, 
which bears against an articular spur (derived from sternite) in the sternal 
articular foramen (this relationship may be real evidence against the 
segmental nature of the first-mentioned calcification). The most distal 
segment, which carries the exopodite and endopodite, is longer than the 
preceding and has a greater transverse width, overhanging its predecessor 
on the medial aspect, i.e. in the region of the medial sternal process. The 
form of this element resembles that of the corresponding segment in the 
pleopods of Bathynomus — see Milne Edwards and Bouvier (1902, pi. vi, 
fig. 1). The sympodite of each of the last two branchise is short and but 
slightly calcified ; no third calcification can be made out in it. 
Reference to fig. 10 will show that the articular foramina in the 
sternites are transversely elongated, that each has an articular spur, that 
the anterior foramina are large and the posterior small, and, finally, that 
the long axis of the posterior two foramina tends to be increasingly 
twisted out of the transverse plane. Some of these points are of importance 
in determining the precise line of modification that has occurred in the 
uropods. 
The muscles that move each sympodite on the body are two in number, 
an extensor and a more powerful flexor. The extensor muscle, very 
slightly broader at its origin from the tergite than at its insertion, passes 
vertically downwards to be attached to the anterior aspect of the first 
complete ring of the sympodite in its middle and lateral part. The flexor 
muscle, posterior to the extensor, thicker, shorter, and more fan-shaped, 
takes origin from the whole lateral part of the tergite and converges to 
a stout tendon inserted into the posterior part of the above segment, only 
more laterally than the extensor. The more medial insertion of the 
extensor muscle as compared with that of the flexor might almost be 
inferred from the appearance of the sternal foramina — see fig. 10. The 
muscles that operate the last two pairs of pleopods are very feeble. 
The Uropods . 
The serial correspondences of the parts of the uropodal appendages of 
Valvifera are apparently still unsettled. In Caiman’s (1909) book we 
* Since this was written I have found Lloyd’s (1908) account of five separate plates in 
the pleopodal sympodite of Indian Ocean forms of Bathynomus giganteus. It would be 
manifestly absurd to apply Hansen’s conception to this case. 
